Longer and Shorter Forms of Sendai Virus C Proteins Play Different Roles in Modulating the Cellular Antiviral Response

Abstract

The Sendai virus (SeV) C gene codes for a nested set of four C proteins that carry out several functions, including the modulation of viral RNA synthesis and countering of the cellular antiviral response. Using mutant C genes (and in particular a C gene with a deletion of six amino acids present only in the larger pair of C proteins) and recombinant SeV carrying these mutant C genes, we find that the nested set of C proteins carry out a nested set of functions. All of the C proteins interdict interferon (IFN) signaling to IFN-stimulated genes (ISGs) and prevent pY701-Stat1 formation. However, only the larger C proteins can induce STAT1 instability, prevent IFN from inducing an antiviral state, or prevent programmed cell death. Remarkably, interdiction of IFN signaling to ISGs and the absence of pY701-Stat1 formation did not prevent IFN-␣ from inducing an anti-Vesicular stomatitis virus (VSV) state. It is possible that IFN-␣ signaling to induce an anti-VSV state can occur independently of the well-established Jak/Stat/ISGF3 pathway and that it is this parallel pathway that is targeted by the longer C proteins.Paramyxovirus P genes are remarkable for the complexity of their genetic organization and expression. This gene, named for the phosphoprotein that is an essential component of the P/L viral RNA polymerase (vRNAP), contains additional open reading frames (ORFs) that overlap the beginning and the middle of the P protein ORF (the C and V ORFs, respectively) ( Fig. 1). The C and V overlapping ORFs are accessed by a variety of unusual mechanisms of ribosomal choice (reviewed in references 9 and 31) and mRNA editing (39, 41), respectively. The overlapping ORFs are also referred to as "accessory" genes (1) because in each case there is at least one virus within the subfamily Paramyxovirinae that does not contain (or express) the V or C genes. For Sendai virus (SeV), a nested set of 2 longer C proteins (CЈ ACG81 and C AUG114) and 2 shorter C proteins (Y1 AUG183 and Y2 AUG201 ) are expressed (Fig. 1). The two longer C proteins (along with the P protein) are initiated by scanning ribosomes, whereas the two shorter C proteins are initiated by a ribosomal shunt (31).The first property of the multifunctional C proteins noted was their ability to modulate viral RNA (vRNA) synthesis. When vRNA synthesis is reconstituted in vitro with purified N:RNA nucleocapsids and the products of the P/C and L genes (expressed in transfected cell extracts), specific ablation of C gene expression (or its replacement with mutant C F170S genes) increases vRNAP specific activity ϳ8-fold (5). The longer CЈ or C proteins are equally active in this respect, but the shorter Y proteins are inactive. The inhibitory effects of C expression are promoter specific, in that genomic promoters are considerably more sensitive to inhibition than antigenomic promoters (1, 38). Remarkably, the negative effects of C on vRNA synthesis are accompanied by an equivalent increase in promoter fidelity, in that minigenomes with promoter mutations (including those wh...

Genetic Analysis of Phosphoprotein and Matrix Protein of Rabies Viruses Isolated in Brazil

“…In five serine residues which constitute the phosphoacceptors in the P protein of the CVS strain [13], Ser 210 and Ser 271 within the PKC phosphoacceptor target were notably conserved in all lyssavirus genotypes (GT 1 to 7) [32], including the Brazilian RV variants examined in this study. Studies on VSV and paramyxovirus have shown that P gene-encoded multiple proteins are important in the viral replication cycle and pathogenicity of the virus [12,24,37]. The four methionine residues located in-frame of single P protein sequences are translated into four proteins of various lengths with no known function in the CVS strain [4].…”

The STAT2 Activation Process Is a Crucial Target of Sendai Virus C Protein for the Blockade of Alpha Interferon Signaling

“…77, 2003 STAT2 ACTIVATION PROCESS AS A TARGET OF SeV C PROTEIN 3367 also the shorter forms (Y1 and Y2) can inhibit IFN-␣ signaling (10,11); however, only the larger proteins prevent establishment of the IFN-mediated anti-vesicular stomatitis virus (VSV) state (10). In contrast, Kato et al have presented evidence for the equal activities of the longer and shorter C proteins for the inhibition of IFN-mediated anti-VSV state, as well as IFN signaling (22).…”

“…In addition to the C protein, the shorter forms, Y1 and Y2, have the ability to inhibit IFN signaling (11,22). The C protein, however, does not lead to degradation of any component on the signaling pathway in most cell types (12,18,24,42,49) except for NIH 3T3 mouse embryo fibroblast (MEF) cells (10,11). The purpose of the present study was to better understand how the SeV C protein inhibits IFN-␣ signaling without degrading cellular proteins on the signaling pathway.…”

Proteolytic Processing and Translation Initiation

“…In particular, all four have been shown to interact with Stat1, an interaction that blocks type 1 interferon signaling to reporter genes carrying interferon-stimulated response elements. However, whereas binding to either CЈ or C leads to proteasomemediated Stat1 turnover and hence a subsequent block on the interferon-induced antiviral state, binding to the Y proteins does not destabilize Stat1, and the antiviral state can be observed (36,45). Our own work suggests that both CЈ and C expression but not Y is detrimental to cell viability.…”